1. Field of the Invention
The present invention relates to an optical disc recycling method and in particular, to a method for recycling an optical disc having a layer containing a metal.
2. Description of the Prior Art
A great amount of optical discs are produced in and out of Japan for various applications such as a so-called compact disc for music, a CD-ROM optical disc for a personal computer, a CD-ROM optical disc for a video game, and a write-once optical disc.
Consequently, even with a small defect ratio, a great amount of defective discs are produced in total to be discarded.
These defective discs have been collected by a discarding company which crushes the defective discs into pieces and throws them away in the ground. This is because it is difficult to recycle an optical disc having layered configuration consisting of a substrate made from an optical transparent resin material such as a polycarbonate, metal layers of a reflection film made from aluminium for reflecting a laser beam and a recording layer made from an optical recording material, as well as a protection layer made from an ultraviolet-setting resin and a label printing layer.
On the other hand, from the ecological viewpoint, an attempt has also been made to recycle these optical discs. For example, the discs to be discarded are crushed as they are mixing the metal layers, protection layer, label printing layer and the like, so as to be used as a molding material. It has also been suggested to remove the metal layer and the other layers from the substrate by way of mechanical polishing or chemical processing, so as to obtain a molding material.
However, the former results in that the recycled resin material contain a plenty of impurities such as metal from the metal layers and has problem that a molded body from the recycled resin material is unstable in bending strength and bending elasticity and its application is limited.
On the other hand, the latter method of recycling enables to obtain a comparatively pure resin material but the mechanical polishing or chemical processing requires an equipment of high costs and has a problem in the processing efficiency. When a chemical processing is employed a plenty of chemicals is to be used, which in turn brings about an ecological problem of secondary pollution.
In a case of write-once optical recording disc such as a CD-R disc, a precious metal such as gold is often used for the reflection layer, but recycling of such a precious metal is not considered in the aforementioned recycling methods. For the CD-R disc, for example, see U.S. Pat. No. 4,940,618 and U.S. Pat. No. 4,990,388.